German Patent Publication No. 3,212,149 describes an angle transmitter in which the stator contains a coil wound along a circular arc and containing a central tap. The coil is seated upon an annular core made of non-magnetic material and having substantially rectangular cross-section. Strips of magnetic material are inserted into the interior surface and into the exterior surface of the annular core. This stator is seated in a flat box-shaped housing. The rotor is journalled in the housing by means of a shaft. The rotor is constructed as a rotary member containing a disc and two coaxial ribs extending along the circumference of the disc. The ribs extend internally and externally around the coil. The rotor is manufactured from non-magnetic material. Strips of ferromagnetic material are sunk into the outer side of the inner rib, into the inner side of the outer rib, which sides face the coil. These strips extend over part of the circumference. The ferromagnetic strips affect the stray field and effect a change in the inductances of the coil portions on both sides of the central tap when the rotor is rotated. A circuit arrangement responds to these changes for generating an angle signal. In the known angle transmitter the rotor can be rotated through full circle. However, an angle signal which is proportional to the rotational angle, can be obtained only through a limited angular range of, for example, 90.degree..
For this reason the known angle transmitter has been provided with a reducing gear. An input shaft is coupled to the rotor via such reducing gear. Therein the input shaft jointly with the reducing gear is seated in a separate housing which is attached to the recited flat housing according to German Patent Publication No. 3,212,149. The output shaft of this gear is coupled to the shaft which carries the rotor. The input shaft, then, can be rotated through 360.degree. or, if required, even through a greater angle, whereas the rotor moves within the range in which a linear angle signal is obtained. The circuit arrangement which responds to changes in the inductances of the two coil portions for generating the angle signal is also accommodated in a separate housing, which is attached to the flat housing of the actual angle transmitter in a practically realized known arrangement of the type according to German Patent Publication No. 3,212,149.
Thus, for the overall arrangement, there result relatively great axial dimensions which are undesired for many uses.
The same problem also occurs in angle transmitters operating according to a different principle, for example, in angle transmitters in which an armature which contains a core of low-retentivity material, more or less widely extends into arcuately wound coil portions and the core is moved farther into the one coil half and correspondingly farther out from the other coil half when the armature is rotatably moved out from a central position.
German Patent Publication No. 3,325,318 describes an incremental angle encoder containing means for optional adjustment of an absolute zero point or reference point. These means consist of a reducing gear which is coupled to the angle encoder shaft on the drive side and on the driven side to a disc comprising an opto-electronically scannable bore or light reflection mark. The disc constitutes a gear wheel which is coupled to the reducing gear by means of a sliding clutch and which can be externally adjusted using a tooth wrench provided with a pinion. The absolute zero point thereby can be adjusted for the incremental angle transmitter.
In this arrangement the disc of the angle encoder, the reducing gear which is constructed as a planetary gear, and the gear wheel are axially series arranged. Thus there results an undesirably great overall length which is a bar to the accommodation in a flat housing.
German Patent Publication No. 2,659,760 shows an arrangement for indicating the angular position of a rotatable member provided with a shaft, for example, the printing head of an office machine. Therein the rotary movement of the shaft which constitutes the input shaft of the arrangement is transmitted to a second shaft by means of a gear wheel transmission in a speed changing manner. A drum containing a photoelectrically operating incremental angle encoder is seated on the second shaft. In this manner only a partial revolution of the input shaft corresponds to a complete revolution of the drum in correspondence with the transmission ratio. Therefore, small angle increments of the input shaft are covered by relatively coarse angle increments of the drum. In order to obtain a zero point which corresponds to a predetermined position of the input shaft, a second drum is arranged within the drum. The second drum is rotatably journalled at the second shaft and coupled thereto via a reducing gear arranged within the interior of the second drum. The reduction is selected such that the second drum is rotated through the same angle as the input shaft. The second drum is also photoelectrically scanned and supplies the zero point.
Both the arrangements according to German Patent Publication Nos. 3,325,318 and 2,659,760 constitute incremental angle transmitters which are driven through a number of revolutions either directly as according to German Patent Publication No. 3,325,318 or via a speed changing transmission as according to German Patent Publication No. 2,659,760. The members driven via a reducing gear do not constitute angle transmitters but only supply a zero point. These arrangements are not concerned with an angle transmitter containing a rotor which cooperates with a stator through a limited angular range for generating an output signal dependent on the rotational angle, and with the accommodation of such angle transmitter, together with the reducing gear in a flat housing.